The present invention generally relates to carbon dioxide dry cleaning systems and, more particularly, to improved carbon dioxide dry cleaning systems that purify and reclaim carbon dioxide without the use of heaters and that do not use pumps to move liquid carbon dioxide.
The dry cleaning industry makes up one of the largest groups of chemical users that come into direct contact with the general public. Currently, the dry cleaning industry primarily uses perchloroethylene (xe2x80x9cpercxe2x80x9d) and petroleum-based solvents. These solvents present health and safety risks and are detrimental to the environment. More specifically, perc is a suspected carcinogen while petroleum-based solvents are flammable and produce smog. For these reasons, the dry cleaning industry is engaged in an ongoing search for alternative, safe and environmentally xe2x80x9cgreenxe2x80x9d cleaning technologies, substitute solvents and methods to control exposure to dry cleaning chemicals.
Liquid carbon dioxide has been identified as a solvent that is an inexpensive and an unlimited natural resource. Furthermore, liquid carbon dioxide is non-toxic, non-flammable and does not produce smog. Liquid carbon dioxide does not damage fabrics or dissolve common dyes and exhibits solvating properties typical of more traditional solvents. Its properties make it a good dry cleaning medium for fabrics and garments. As a result, several dry cleaning systems utilizing carbon dioxide as a solvent have been developed.
U.S. Pat. No. 4,012,194 to Maffei discloses a simple dry cleaning process wherein garments are placed in a cylinder and liquid carbon dioxide is gravity fed thereto from a refrigerated storage tank. The liquid carbon dioxide passes through the garments, removing soil, and is transferred to an evaporator. The evaporator vaporizes the carbon dioxide so that the soil is left behind. The vaporized carbon dioxide is pumped to a condenser and the liquid carbon dioxide produced thereby is returned to the refrigerated storage tank.
The system of Maffei, however, does not disclose a means for agitating the garments. Furthermore, because the system of Maffei does not disclose a means for pressurizing the chamber, the carbon dioxide must be very cold to remain in a liquid state. Both of these limitations inhibit the cleaning performance of the Maffei system.
U.S. Pat. No. 5,267,455 to Dewees et al. discloses a system wherein liquid carbon dioxide is pumped to a pressurized cleaning chamber from a pressurized storage vessel. The cleaning chamber features a basket containing the soiled garments. The interior of the basket includes projecting vanes so that a tumbling motion is induced upon the garments when the basket is rotated by an electric motor. This causes the garments to drop and splash into the solvent. This method of agitation, known as the xe2x80x9cdrop and splashxe2x80x9d technique, is used by the majority of traditional dry cleaning systems. After agitation, a compressed gas is pumped into the chamber to replace the liquid carbon dioxide. The displaced xe2x80x9cdirtyxe2x80x9d liquid carbon dioxide is pumped to a vaporizer which is equipped with an internal heat exchanger. This allows xe2x80x9ccleanxe2x80x9d gaseous carbon dioxide to be recovered and routed back to the storage vessel.
While the system of Dewees et al. overcomes the shortcomings of Maffei, namely, the lack of an agitation means and a pressurized cleaning chamber, it relies upon a pump to move its liquid carbon dioxide and utilizes a heat exchanger in its vaporizer. Both of these components add complexity, cost and maintenance requirements to the system.
Many patents have disclosed improved agitation arrangements for carbon dioxide dry cleaning systems. For example, U.S. Pat. No. 5,467,492 to Chao et al. discloses a fixed perforated basket combined with a variety of agitation techniques. These include xe2x80x9cgas bubble/boiling agitationxe2x80x9d where the liquid carbon dioxide in the basket is boiled, xe2x80x9cliquid agitationxe2x80x9d where nozzles spraying carbon dioxide tumble the liquid and garments, xe2x80x9csonic agitationxe2x80x9d where sonic nozzles create agitating waves and xe2x80x9cstirring agitationxe2x80x9d where an impeller creates the fluid agitation. The remaining portion of the system of Chao, however, does not provide for a significant improvement over Dewees et al. in that a pump is still relied upon to move the liquid carbon dioxide from the system storage container to the cleaning chamber.
U.S. Pat. No. 5,651,276 to Purer et al. discloses an agitation technique which removes particulate soils from fabrics by gas jets. This gas agitation process is performed separately from the solvent-immersion process. Purer et al. further disclose that carbon dioxide may be employed both as the gas and the solvent. U.S. Pat. No. 5,669,251 to Townsend et al. discloses a rotating basket for a carbon dioxide dry cleaning system powered by a hydraulic flow emitted by a number of nozzles. This eliminates the need for rotating seals and drive shafts. While these two patents address agitation techniques, they do not address the remaining portion of the dry cleaning system.
Finally, the Hughes DRYWASH carbon dioxide dry cleaning machine, manufactured by Hughes Aircraft Company of Los Angeles, Calif., utilizes a pump to fill a pressurized cleaning chamber with liquid carbon dioxide. The cleaning chamber contains a fixed basket featuring four nozzles. As the basket is being filled with carbon dioxide, all four nozzles are open. Once the basket is filled, however, two of the nozzles are closed. The remaining two open nozzles are positioned so that they create an agitating vortex within the basket as liquid carbon dioxide flows through them. Soil-laden liquid carbon dioxide exits the basket and chamber and is routed to a lint trap and filter train. Furthermore, the system features a still that contains an electric heater so that soluble impurities may be removed.
While the Hughes DRYWASH system is effective, it also suffers the cost, maintenance and reliability disadvantages associated with a liquid pump and an electrically heated still.
Accordingly, it is an object of the present invention to provide an improved carbon dioxide dry cleaning system that utilizes both the solvent properties of carbon dioxide and agitation to remove insoluble particles.
It is a further object of the present invention to provide an improved carbon dioxide dry cleaning system that moves liquid solvent without the use of a pump.
It is a further object of the present invention to provide an improved carbon dioxide dry cleaning system that is economical to operate.
It is still a further object of the present invention to provide an improved carbon dioxide dry cleaning system that filters and distills its solvent.
These and other objects of the invention will be apparent from the remaining portion of the Specification.
The present invention is directed to a liquid carbon dioxide dry cleaning system that moves liquid carbon dioxide without the use of a pump. Because liquid carbon dioxide, when used as a solvent, is at a high pressure and in a saturated state, suitable pumps are expensive and not nearly as reliable as devices used for ambient temperature liquids.
A first embodiment of the system features a pair of storage tanks containing liquid carbon dioxide. A compressor initially is connected in circuit between the head space of one of the storage tanks and a sealed cleaning chamber containing the objects being dry cleaned. The liquid side of the storage tank is connected to the cleaning chamber. As a result, the storage tank is pressurized so that liquid carbon dioxide flows from it to the cleaning chamber.
Next, the compressor is placed in circuit between the storage tanks so that gas may be withdrawn from the now empty storage tank and used to pressurize the other storage tank, also filled with liquid carbon dioxide. The liquid side of the empty storage tank remains connected to the cleaning chamber while the liquid side of the full storage tank is connected to cleaning nozzles within the cleaning chamber. As a result, when the full storage tank is pressurized, liquid carbon dioxide flows from it, through the nozzles and into the cleaning chamber so as to agitate the objects being cleaned. The displaced liquid carbon dioxide from the cleaning chamber flows back to the empty storage tank.
The agitation pressure may be controlled so that delicate objects may be cleaned without damage. Solvent additives may also be injected into the liquid carbon dioxide.
A still, submerged in the liquid carbon dioxide within one of the storage tanks, receives soiled liquid carbon dioxide from the cleaning chamber. Gas is withdrawn from the still by the compressor and is used to pressurize the storage tank containing the still. Alternatively, the still may be connected to the liquid side of a low pressure transfer tank. As a result, gas from the still is returned to the transfer tank where it is recondensed by the cold liquid carbon dioxide contained therein. In either case, the pressure difference created between the still and storage tank causes the soiled liquid carbon dioxide to boil due to the heat supplied by the liquid carbon dioxide surrounding the still. This removes the carbon dioxide in gaseous form leaving the contaminants in the still. Heat is also removed from the liquid carbon dioxide surrounding the still without reducing the heat in the system and without mechanical refrigeration.
An alternative embodiment of the present invention includes a cleaning chamber containing objects to be cleaned and a storage tank containing a supply of liquid solvent such as liquid carbon dioxide. A compressor pressurizes the storage tank with gas from the cleaning chamber so that liquid solvent is delivered to the cleaning chamber through nozzles. The cleaning chamber includes a basket rotatably mounted therein for agitating the objects during one or more prewash and wash cycles. A transfer tank contains an additional supply of liquid solvent and selectively communicates with the cleaning chamber so that additional solvent may be added to the system.
The system features a still containing contaminated liquid solvent received from the cleaning chamber after a previous prewash cycle. The cleaning chamber is pressurized with gas from the still so that the contaminated liquid solvent in the still is vaporized and transferred to said cleaning chamber. The compressor may be used to accelerate this process. The still may be equipped with a steam supply line or other heating means for improved boiling. The still may optionally be placed within the storage tank and partially surrounded with a shroud to direct warm gas from the compressor as it withdraws gas from the cleaning chamber to efficiently heat the still promoting the boiling of the contaminated liquid within.
The system includes a filter for filtering liquid solvent from the wash chamber after each wash cycle. A dispenser injects additives such as detergent and softeners into the liquid solvent exiting the filter. One or more prewash cycles may be performed after which liquid solvent from the cleaning chamber bypasses the carbon portion of the filter and travels directly to the still.
During the wash cycles liquid solvent may be withdrawn from the cleaning chamber, filtered and returned to the cleaning chamber so that constant filtration is provided. Solvent gas may be withdrawn from the storage tank so that the liquid therein boils. The resulting vapor may be raised in pressure and temperature by the compressor and introduced into the liquid solvent in the cleaning chamber so that the liquid solvent is warmed and its cleaning properties are enhanced.
Pressure relief valves are positioned between the cleaning chamber and the head space of the storage tank and the filter and the head space of the storage tank to relieve pressure in the cleaning chamber and filter in the event of an emergency system shutdown without venting gas to the atmosphere.